Rubber processing



United States Patent-"G p aw mApp icafion than; 511". Serial No. 361,43, t 8 Claims. 01. 2 0741.57 t.

This invention-relates to improvementsin theiechnique of processing. mixtures of natural rubber or GR% and carbon black prior to vulcan-ization thereof.

The ch e-0 rw es insit bb r m redw hrs aw tively large amounts of reinforcing earbonbl-ack,-- v vhere b q i zat s hd p qve p ysiaal'a d t em ical properties, is described in Gerke et aL- U. 5, Pat 2,118,601. ,The improved vulcanizate sjprepared: by;;th technique of Gerke et al. differ fromthe usual vulcaniza ada ed hr e der: t hn n .t t e h r -in ate owermodulus at lowe g t m (ll hsfi' 3 5. about ,\300% elongation, (3) higher resista t sion,;.. (4) lower. torsional. hysteresis,l and 5) we I triealvresistivi ry, and are: (6) relatively spfter These improved vulcanizates are obtained y incorpo t a i or in thew b a at w alatsea tq owing-carbon, black for example; atlleastp t-t da eie b r -.-in s of t t ads, a le st;

weight of rubber, and thenrsubjecting-the =unifor mly,rnixed;.--;

masterbatch to a special heat treatment at a temperaturee cial heat treatment may. ,vary, with l the temperature em;

ployeql, th q highfi fihettemperature, the shorter --the time,,

and is governedhalso by the degreeuof change desired in H the properties of the ultimate vulcanized product which properties are gauged to be compatible with its final use.

In general, heat treatments offrom 10 to 60 minutes 7 rat snr W b .fmmd s itable ar. mo t, p moses ..p r-. ticul-arly when the heat treatment is carried outby masticag. M tion within the'preferred temperature range. I

An object or" the tpresent invention is to provide,j ,ehemicals which strongly influence and/ or augmentthetefiecte of heat treatn ient of theytype-referred to above;';; rubber-carbon blackmasterbatehes sStated.difierentl y,-: an object of theg invention is to provide catalysts capable {of materially promoting tlie benefits of heat treating. rub carbon black -m-asterbatches whereby even greatler provements in tread wearlandhysteresis properties: can h achieved"; Numerous other objects of the present, invention will more fully hereinafter appears c a ese e n mia i l b s d u on m d s o -sha inorganic peroxidiescomponnds selected from :th gr-gnp t-rr consisting of Qthe peroxides of zinc, magnesium, calcium,

strontium and barium, and potassium persulfa'te'are effective' 'catalysts or promoters of the heat treatment at high temperatureof carbonblack masterbatches in'accordy ancewi-th' the technique of Gerke et a1. 2,1 '18;60 1,'whereby greater; reduction in torsional hysteresis is achieved by the heat treatment.

More specifically,- my, invention resides in a method of making-rubber products and-particularly tire: treads, =by I heating intimate mixture of natural rubber or rubbery copolymer of butadiene andstyrene typiiledby' GRe-S, or a mixt r ,a t tal ub 3. 15131! T bb' I S PQh QIQ o bbetiatqr ns ar onsbl a a inq saei 'P I'QX-JJ t z ompau diwm; 6 a e ta asi a mae a r tleashzlfi t i -afl aem a 11y, injure the properties of the rubber to a time uifig nt g substantially lower the torsional hysteresis of a vulcanizate New Jersey 0 ICC either resulting mixture, masticating theresulting mixturev compounding" ingredients, shaping, and vulcanizingm Theitemperature at whichthe, heat, treatment. is con dugted will generally not exceed 450 C.. V

Byperforming the heat -,tr.eatmentlof the carbon blacltrubber masterbatch -in ,the presence, of, the inorganic pe oxidi c eornpounivulcanizates having; materially lower hvsteresis are' obtainedi It is generally kconsideredsthat h reductions in torsional hysteresis of the order of 01 more are sufficiently; great .to be. commercially important. Myi-nvention makes it easily, possible, to vobtain:r -ednct ions1, in torsional hysteresis, considerably greatenrthan;.01,..--; It may be notedt at this-point that the torsional hysteresis of, conventionally:processed tread-stockusually ranges-fron a .1 to ,15. Values below,.08usually indicatethat a.non:--'

conyentionall hot processing r-hasbeen; employed --i-n 5 the; y manufacture of the carbon black-masterbatch'from.which I .rttt d-z t tkx "m -1 1 Thesmaterially-lower torsional hysteresis-brought about:

by the practice of my invention is usually accompaniedby :z,

a significantly-higher. electrical" resistivity of the? resulting} vulcanizate It is also accompaniedaby':improved wear--2- resistance which -becomes apparent .under specially-severe driving-conditions where heat 'generationsais: an im'portant faeton-aThus; the improved wear PIOPEliifiS'LOf =vulean-*, izates,,- made 1in accordance --=with-- mytinvention tdo *not manifiest themsel-yes under ordinaryadriving conditionsyforli example at relatively low speeds or at relativelymoderate a atmospheric? temperatures:v However, they do; manifest themselvesfnnder very: severe t driving conditions such as are; tencoun-teredrin the'southwestern :and western portions 1 in glyprevalent everywhere because of theincrea'sed avail abilitjniof highi-speedh'ighway-s and high speed vehicless In one. method of practicing my invention, 1 firstp're-t parezin the'Banbury mixer or-on theopen'rubb'er mill t carbon blaclc rlubber masterbateh containing intimately dispersed therethrough a smallamount -of'the'=;inorgani c-' peroxidiev compound, and, if desired, also 'cOntaining-cOnventional amountsfiof any desired 'non-v'uleanizjng compounding"ingredientasuch as small amounts of a softenen fattylacidvie mg s-tearieacid, 'zinc saltof fatty aeid,'-e, 'g,, zinealaurat'e, etc.-- In preparing this masterbatch I' prefer 5 to ernploy stook'temperatures of at lea'st 275 F. during; "a considerable portion, say at least 5 minntes', of the:

0 substantial period c-f time, say'f or frotn' 1 to 24 h onrs a t a temperature of at least 275 F. 'until the properties lof thefstockhaye been, so'eh anged that the torsionalh'ys;

' teresisof a'yulcanizate of the resulting mixtu e is sub;

I YI IIh E t at s 'v qatiizate o a ampa le 5 mixtlttre made "injthe conventional manner. Afterpthe' *heat'treatment, the stock is re-milled in a rubber million a Banbu m er, u l a lativ ly. l mpst wrest e a St empera u es o t v qm. 1. 0m 200. r 1? l fii a ti e sa mm l o ,1. in t l y ti tiinse f et p oduced yrt h tt a n t s il ("out h This re milling eauses the batch toarecoverrtoa smooth plastic consistency. Thereupon the vu1canizingingredients,e. g. sulfur, accelerators, etc. andany,other desired compounding, ingredients, aresi-ntimatelydncorpo rated ata relatively lowstock temperature,.viz .-not.over.; *ZSQfl R, whereupontthe resulting stock sis shaped and lsaaizad n eu a w -s Instead of conducting the heat treatment by mastica tion followed by static, holding at temperatures offat least 275-? F., .I. can perform .theheat;treatmenuentirely byg: a tiw anp t ta t h ld n -r e pre edurez-i wherein the'bulk of theheat treatment takes place under static conditions lends itself especially well to factory operation because of the economies thereby effected, it being much cheaper to heat treat statically than by mastication, as on an open rubber mill or in a Banbury mixer.- Instead of the modes of procedure which have been mentioned, I could conceivably heat treat firststatically and then with mastication or I could employ alternate static and masticatory heat treatments. If the last portion of the heat treatment is done statically, it is necessary to re-mill the stock to smooth it out before incorporating sulfur and other vulcanizing ingredients. If the last portion of the heat treatment is carried out by milling or mastication, it is prolonged usually at a lower temperature, say at 100-250 F., until the stock smooths out.

In practicing my invention I particularly prefer to employ a temperature of at least 350 F. in performing the heat treatment, or at least during a substantial portion thereof. Thus, I can mix in a Banbury mixer at a stock temperature of at least 350 F., say 350-450 F., for to 60 minutes and follow this by static treatment at a lower temperature, say 275-325 F., for a suitable length of time, say 1 to 24 hours.

The duration of the heat treatment will vary, depending upon many factors, including the temperature at which it is conducted, the type of mixture, the amount and type of inorganic peroxidic compound used, whether the heat treatment is performed statically or with mastication, etc. In the case of solely static treatment, times ranging from 1 to 24 hours are commonly employed. In the case of solely masticatory heat treatment, times of the order of 5 to 60 minutes at temperatures of 325-450 F. are usually sufficient. It will be obvious that time and temperature are generally inversely related.

Any of the reinforcing carbon blacks can be used in the practice of my invention. Both furnace blacks and channel blacks are commonly used for reinforcing carbon black and can be used in my invention. The amount of carbon black present during the heat treatment should equal at least 25 parts per 100 parts by weight of rubber. I prefer that the amount of carbon black be equal to at least 40 parts per 100 parts of rubber, the use of such high proportions of carbon black being particularly suitable in the case of tread stocks.

I particularly prefer to employ the peroxides. of zinc, magnesium, calcium, strontium and barium. Of these peroxides, I much prefer to employ zinc peroxide because it assures an excellency of hysteresis properties, especially if-i t is present during mastication of the rubber in the presence of the carbon black at temperatures of the order of 360 F, and higher. In addition, zinc peroxide appears to function as a replacement for zinc oxide which is a fairly expensive filler. This serves to substantially offset the relatively high cost of zinc peroxide.

a mixture of rubber and zinc peroxide be subjected to the heat treatment in the absence of'the carbon black, there is little if any effect upon the hysteresis of the vulcanizate of the mixture obtained upon incorporation of carbon black with the heat treated mixture.

The following examples illustrate my invention in more I detail:

Examples 1 to 6 The following stocks were first prepared in the usual way, in a Banbury mixer:

Example 1 2 3 4 5 6 Smoked Sheets 90. 40 90. 40 90. 40 90. 40 90. 40 90. 40

e0 .50 Zinc Peroxide 5O 50 50 Banbury Discharge Temperature, F L 320 340 385 295 350 400 The mixing in the Banbury was continued only long enough to give an intimate uniform mixture. The Banbury was discharged with the stocks at the temperature indicated in the table whereupon the stocks were sheeted out to a thickness of 100 gauge. The sheeted stocks were then heat-treated statically for two and one-half hours in an atmosphere of steam at 500 p. s. i. gauge (approximately 298 F.). The resulting stocks were then remilled in the Banbury for 4 minutes to eliminate their stiffness and prepare them for compounding. The viscosities of the resulting stocks were:

Mooney Viscosity (LR) 82. 5 84. 5

-The stocks were then compounded with conventional Instead of the metallic peroxides mentioned above, I

can use potassium persulfate.

The amount of the peroxidic compound used in the practice of my invention can vary widely. However, almost invariably the amount is not less than 0.3 nor more than 3.0 parts per 100 parts by weight of rubber. Amounts less than 0.3 part are not sufiicient and amounts above 3.0 parts are too costly.

In the practice of my invention, the use of zinc peroxide and a masticatory heat treatment at a temperature of at least 360 F., and preferably at least 400 F., gives an unusual synergistic eifect and produces maximum lowering in hysteresis and maximum increase in electrical resistivity. Thus, a preferred mode of practicing my invention involves masticating the rubber-carbon black-zinc peroxide amounts of sulfur and accelerators and vulcanized in the usual way. The vulcanizates had the following properties:

Example 1 2 3 4 5 6 300% Modulus, p. s. i.:

30' cure 2,530 2,820 2,630 2,490 2.700 2,730 2,860 2,820

067 069 90' cure; .094 .096 .079 .087 .079 073 Log of Electrical Resistivity (ohm-centimeters) 30 9.98 10.01 12.64 11.46 12.34 13.04 45 cure 9.63 12.21 11.06 11.84 13.04 90 cure 9.44 11.90 12.06 11.90 l3.04

The vulcanizates of Examples 4 to 6 had higher abrasion-resistance, as measured on the laboratory abrader, than those of Examples 1 to 3. In general the laboratory abrasion ratings follow rather closely .the trends noted in connection with electrical resistivity. That is, higher resistivity and improved abrasion rating tend to accompany the use of both zinc peroxide and higher Banbury temperatures in the carbon black masterbatch mixing.

.The material reduction in torsional hysteresis of stocks 4 to 6 is to be noted. A reduction of .002 or more in this test is considered significant and important. The accompanying marked increase in electrical resistivity in stocks 4 to' 6 is to be noted. The data show that greatly im:

proved physical properties result from the use of the zinc peroxide in stocks4 to 6.

s r meanders-"not r es's stoiilis 3')"- tlie resistivity-reaches amaxiinuiii 'af or before the 30- ifliniit'e sure and thereafter falls of! with increasing time of vulcanization. In the sewer the zinc perbxide a'ctb vats- 1 stbclci's (Examples l' to '6)" the res 'eet'e'nds to remain riibrenea'rly-"cons'tfn't u'p t'o theso-mmmecure, showing, if aiiythin'g, a sliglitinoiea tures Were-BOO E1, 355 Rami- 4'00 respectively.

Example 300% Modulus:

Examples to 13 Example 6 was duplicated, using,0.5, 1.5 and 3.0 parts 60 lbs. gauge (approximately 308 F. mthe static heat treatment. Example 13 was acontrol; in which-the zinc peroxide was replaced with 0.5 part of zinc oxides, The data on the vulcanizates were as follows:

Example 10 11 l2 13 Amount of ZuOz used 5 1. 5 3. 0 Torsional Hysteresis:

cure 074 069 070 078 45 euro. .n. 068 069 070 073 90 cure 070 070 076 76 300% Modulus, p. s.

30' euro 2, 500 2, 520 2, 520 2, 470 2, 620 2, 680 2, 300 2, 800

3, 420 3, 900 3, 260 3, 940 2, 720 a, 700 Elongation:

80 cure 400 395 375 435 45 cure 305 370 360 405 90 cure 345 340 340 370 Examples 14 and 15 Example Smoked sheets Balata Stearic Acid Zinc Laur Zinc Oxide Zinc Peroxide. 1.

Emmi-fin 14 p 300% Modulus:

30 r-11m. v 2 449. 45" eur 2, 800 905 r 4.. 2 700. Tensile:

cur 4,030 45tcur I 3,1650 "0nmz- 1 e. r, 3 590) Elongation: 30 eur 1 The marked r'eduetioniii torsional hysteresis vulcaniz'ate of Example 15 whichwas activated wi'tl'i'liiiic peroxide compared to Example 14 is noteworthy;-

Examples "16 to 21 Example In preparing the mixtures, the rubber was allowed to band and heat up to the mill roll temperature before incorporating the other ingredients. In Examples 16 to 18 the milling time was only that required to yield a uniform mixture, while in Examples 19 to 21 the milling was continued for the additional period indicated in the above table.

The resulting mixtures were then compounded in the conventional manner with sulfur and other compounding ingredients and vulcanized. The vulcanizates had the following properties:

Example 16 17 18 19 20 21 300% Modulus, p. s. 1.:

30' cure 2, 2, 440 2, 380 2, 440 2,440 45 cure 2, 590 2, 64 2, 650 90 cure 65 Tensile, p

30' 3, 260 2, 820 3, 020 2, 360 45 cure 2, 830 3, 200 3,030 2, 390 90' euro 2, 430 2,700 2, 520 1, 920 Elongation:

30 cure 500 480 385 333 357 300 473 413 317 345 323 280 415 360 280 300 285 240 It will be seen that the purely masticatory treatment with zinc peroxide (Examples 18 to 21) gave a significantly lower torsional hysteresis than the same treatment with zinc oxide (Example 17).

. Examples 22 to 27 These examples show the effect of static heat treatment in addition to the masticatory heat treatment of Examples 16 to 2'1. Portions of the hot milled stocks of Examples 16 to 21 were subjected to static heat treatment for two and one-half hours at the temperature of steam at 50 p. s. i. gauge. The resulting stocks were then re-milled in a Banbury' mixer for 4 minutes after which the same vulcanizing and other compounding ingredients as.were used in Examples 16 to 21 were incorporated, followed by vvulcanization.

The following data were obtained:

;Example 22 23 24 25 26 27 Mooney Viscosity Before ,collnfounding 61.5 54 53 45.5 41.5 37

300% odulus, p. s. i.:

so I 2,630

TenslleJ Elongation Comparison of these data with the data for Examples 16 to 21 shows that a static heat treatment following masticatory heat treatment in the presence of zincv peroxide gives a further substantial reduction in torsinal hysteresis. Having thus described my invention, what I claim and desire to protect by Letters Patent is: 1. A method of manufacturing rubber products which comprises heat treating an intimate mixture of a rubber selected from the group consisting of natural rubber and butadiene styrene rubbery copolymers, a rubberreinforcing carbon black and an inorganic peroxidic compound selected from the group consisting of the peroxides of zinc, magnesium, calcium, strontium and barium, and potassium persulfate at a temperature of at least 275 F. but insufliciently elevated to substantially injure the prop- I erties of the rubber for a time sufiicient to substantially lower the torsional hysteresis of a vulcanizate of the resulting mixture, masticating the mixture and incorporating vulcanizing and other desired compounding ingreditemperature.

4. The method of claim 1 wherein said heat treatment is carried out by masticating said mixture at said temperature and then holding the mixture under static conditions at said temperature.

5. The method of claim 1 wherein said compound is zinc peroxide.

6. The method of claim 1 wherein said compound is zinc peroxide and wherein said heat treatment is at least partially performed by mastication at a temperature of at least 360 F. v

7. The methodof claim 1 wherein said compound is potassium persulfate.

8. Themethod of manufacturing rubber products which comprises masticating at a temperature of 350 to 450 F. a mixture of a rubber selected from the group consisting of natural rubber and butadiene-styrene rubbery copolymers, at least 40 parts of a rubber-reinforcing carbon black per parts of said rubber, and from 0.3

to 3.0 parts of'zinc peroxide per 100 parts of said rubber, sheeting the resulting stock, and heat-treating the sheeted stock at a temperature of from 275 to 325 F. while holding it under static conditions, the efiect of the masticatory and static heat treatment being to substantially lower the torsional hysteresis of a vulcanizate of the resulting mixture, re-milling the resulting stock, incorporating vulcanizing and other desired compounding ingredients, shaping, and vulcanizing.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF MANUFACTURING RUBBER PRODUCTS WHICH COMPRISES HEAT TREATING AN INTIMATE MIXTURE OF A RUBBER SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER AND BUTADIENE-STYRENE RUBBERY COPOLYMERS, A RUBBERREINFORCING CARBON BLACK AND AN INORGANIC PEROXIDIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE PEROXIDES OF ZINC, MAGNESIUM, CALCIUM, STRONTIUM ABD BARIUM, AND POTASSIUM PERSULFATE AT A TEMPERATURE OF AT LEAST 275* F. BUT INSUFFICIENTLY ELEVATED TO SUBSTANTIALLY INJURE THE PROPERTIES OF THE RUBBER FOR A TIME SUFFICIENT TO SUBSTANTIALLY LOWER THE TORSIONAL HYSTERESIS OF A VULCANIZATE OF THE RESULTING MIXTURE, MASTICATING THE MIXTURE AND INCORPORATING VULCANIZING AND OTHER DESIRED COMPOUNDING INGREDIENTS, SHAPING, AND VULCANIZING. 